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Herein, the temperature dependence of hysteresis loops and the Giant magnetoimpedance, GMI, effect of amorphous as-prepared and stress-annealed FeSiBC microwires have been thoroughly analyzed. We observed a remarkable improvement of GMI ratio and modification of hysteresis loops from rectangular to inclined with increase in temperature for as-prepared FeSiBC microwires. Observed changes have almost completely reversible character. On the other hand, rather different behavior is observed in stress-annealed FeSiBC microwires: a substantial GMI ratio improvement is observed in stress-annealed FeSiBC microwires. However, a decrease in GMI effect is observed with temperature increasing. Observed experimental results are discussed considering relaxation of internal stresses upon heating, Hopkinson effect and modification of the thermal expansion coefficients upon heating. • Strong temperature dependence of hysteresis loops and Giant magnetoimpedance effect of Fe 75 B 9 Si 12 C 4 glass-coated microwires. • Almost complete reversibility of the hysteresis loops and GMI effect modification upon heating of as-prepared FeBSiC microwires. • Substantial improvement of the GMI ratio with increase in temperature for as-prepared FeSiBC microwires. • Temperature dependence of the GMI effect in Fe-rich microwires useful for temperature monitoring. [ABSTRACT FROM AUTHOR]

We have fabricated fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPPGMR) devices using C1b-half Heusler compound NiMnSb, the first candidate of the half-metallic material, as the electrode with a Ag spacer. The device shows magnetoresistance ratios of 25% at 4.2K and 9.6% at 290 K, which are one of the highest values for the CPP-GMR with half-Heusler compounds. However, these values are much lower compared to those reported for CPP-GMR devices with L21-full Heusler compounds. Careful analysis of the microstructure using scanning transmission electron microscopy and energy dispersive spectroscopy through the upper NiMnSb/Ag interface indicates the heterogeneous formation of Ag-rich solid solution or the island growth of Ag on top of NiMnSb, which clarified a difficulty in evaluating an intrinsic spin-polarization in NiMnSb from CPP-GMR devices. Thus, to evaluate a spin-polarization of a NiMnSb thin film, we fabricated non-local spin valve (NLSV) devices using NiMnSb with Cu channel wires, which is free from the diffusion of Cu to NiMnSb because of no annealing proccess after deposition of Cu. Finally, intrinsic spin polarization of the NiMnSb single layer was extrapolated to be around 50% from NLSV, suggesting a difficulty in obtaining half-metallic nature in the NiMnSb epitaxial thin film. [ABSTRACT FROM AUTHOR]

The “magnetic differentiation” technique is an original method for magnetic-field measurement. It is used for giant magnetoimpedance (GMI) sensors. The response is very different from the classical impedance measurement. To measure the external field \textH\mathrm {ext} , small increments of magnetic field, alternatively positive and negative \pm \Delta H , are added to H_{\mathrm {ext}} by a small coil around the GMI wire. The measured signal is the slope of the curve of the impedance Z(H_{\mathrm {ext}})$ . The “magnetic differentiation” technique exhibits many advantages. The obtained response is a relatively simple curve with an odd symmetry. The zero of the sensor exactly corresponds to the zero magnetic field. The sensor is able to measure the “absolute zero” field, without any zero-adjustment. Around the zero-field point, the response is linear for a range of several tenths of A/m, with a very high sensitivity. The sensor response around the zero stays constant when the GMI wire is submitted to variable influence parameters, such as temperature or strain. Moreover, the measurement of high magnetic field can be easily made with an additional coil supplied by a closed-loop system; the operation point remains around the zero-field. Globally, the magnetic differentiation technique is an original way of using the GMI effect. The null signal at zero magnetic field, the linearity around the zero, and the odd response are very interesting properties, allowing the development of a new generation of GMI sensors. [ABSTRACT FROM AUTHOR]

Giant magnetoimpedance (GMI) has been proposed as a powerful technique for biosensing. In GMI biosensors based on the magnetic label detection the change of the impedance of sensitive element under the application of an external magnetic field was analyzed in the presence of magnetic nanoparticles in a test solution. Amorphous ribbon-based GMI biodetectors have an advantage of low operation frequency and low cost. In this work, magnetic and GMI properties of amorphous Co68.6Fe3.9Mo3.0Si12.0B12.5 ribbons were studied in as-quenched and surface modified states both without and in the presence of maghemite ferrofluid. After the surface modification the coercivity was slightly increased and saturation magnetization decreased in good agreement with increase of the surface roughness, a decrease of magnetic elements concentrations in the surface layer, and formation of a surface protective oxide layer. The GMI difference for as-quenched ribbons in absence and in the presence of ferrofluid was measurable for the frequency range of 2 to 10 MHz and the current intensities of 1 to 20 mA. Although the proposed surface modification by the ultrasound treatment did not improve the sensitivity limit for ferrofluid detection, it did not decrease it either. [ABSTRACT FROM AUTHOR]

Monitoring the rate of respiration and its pattern is crucial to assessing an individual’s health or progression of an illness, creating a pressing need for fast, reliable and cost-effective monitors. We present here a novel respiratory monitoring technology based on a magnetic microwire coil (MMC) magneto-LC resonance sensor. The 3 mm diameter coil is wound from a melt-extracted amorphous Co 69.25 Fe 4.25 Si 13 B 12.5 Nb 1 microwire. Unlike typical solenoids, the MMC is sensitive to small magnetic fields due to a significant change in an impedance attributed to the high-frequency giant magneto-impedance (GMI) effect. We propose an application of the MMC sensor to detect a position-varying source of a small magnetic field (∼0.01–10 Oe) for real-time respiratory monitoring of a human patient. We simulate this application by mounting a small permanent magnet to a mechanical vibrator and vibrating the magnet at different frequencies, amplitudes, and waveforms ∼3–15 cm above the MMC. This newly developed MMC magneto-LC resonance technology is highly promising for active respiratory motion monitoring and other biomedical field sensing applications. [ABSTRACT FROM AUTHOR]

This article reports a novel separable bioanalyte detection system that combines magnetic nanoparticle labels with giant magnetoimpedance (GMI). The GMI sensor was fabricated via standard microfabrication techniques, and a micro-solenoid coil was integrated with the sensing elements to amplify the signal tags. To verify the feasibility of this strategy, streptavidin-coupled Dynabeads and a-fetoprotein (AFP) bioconjugates were utilized as model analytes, while double antibody sandwich immunoassays and streptavidin-biotin binding assays were employed to immobilize and label AFP on an Au-film coated wafer. The resulting biosystem exhibited markedly improved sensitivity compared to other similar biosensors: A minimum detectable limit of 3 ng/ml for streptavidin-coupled Dynabeads and 0.2 ng/ml for AFP were achieved, respectively. In addition to its very high detection sensitivity, the proposed biosystem can be conveniently manipulated, is not contaminated or damaged by chemical solutions, and is reusable without cleaning. The results presented here may considerably enhance the practical applications of GMI sensors in bio-magnetic-field sensing. [ABSTRACT FROM AUTHOR]

The equivalent magnetic noise spectral density of giant magnetoimpedance (GMI)-based sensors exhibits a low-frequency excess noise inversely proportional to the frequency (1/f noise). In order to enhance the performance and reach the ultimate and intrinsic limit of the magnetometer, it is necessary to investigate the origin of this excess noise. Cross correlation measurements have permitted the demonstration that the excess low-frequency noise arises from the sensor, under defined excitation conditions, particularly the amplitude of the excitation current and the dc bias current. Given that the GMI effect is based on an impedance variation governed by the magnetization direction under an applied external magnetic field, the low-frequency magnetization fluctuations within the GMI wire have been considered to be a possible noise source. The fluctuation-dissipation theorem permits evaluation of the spectral power density of these fluctuations, which is proportional to the imaginary part of the susceptibility, \chi ^\prime \prime . The latter may be evaluated by two different methods, based on the measurement of the real part of the wire impedance and on the evaluation of the circumferential hysteresis loop area. The results obtained by both methods are compared and discussed. The values of \chi ^\prime \prime thus obtained are then used in order to predict the equivalent magnetic noise level at 1 Hz, and are compared with that measured at 1 Hz. The comparison is conducted for different amplitudes of the dc bias current, and the results obtained indicate that the proposed methods have the potential of predicting the excess noise in GMI sensors. [ABSTRACT FROM PUBLISHER]

We present an overview of the factors affecting soft magnetic properties and giant magnetoimpedance (GMI) effect of thin amorphous wires. Low coercivity and high GMI effect have been observed in as-prepared Co-rich microwires. We showed that the magnetoelastic anisotropy is one of the most important parameters that determines the magnetic softness and GMI effect of glass-coated microwires, and annealing can be very effective for manipulation of the magnetic properties of amorphous ferromagnetic glass-coated microwires. After annealing of Co-rich microwires, we can observe the transformation of inclined hysteresis loops to rectangle and coexistence of fast magnetization switching and GMI effect in the same sample. We demonstrated that the switching field value of microwires can be tailored by annealing in the range from 4 to 200 A/m. On the other hand in Fe-rich FeCuNbSiB microwires after appropriate annealing, we observed considerable magnetic softening and GMI effect enhancement. [ABSTRACT FROM AUTHOR]

An anisotropy of the magnetoresistance with respect to the direction of the current is observed experimentally when the magnetic field lies in the plane of a two-dimensional system and is perpendicular to the direction of the current. This effect is related to the combined action of the Lorentz force, which causes a shift in the peak of the electron density from the center to different walls of a quantum well for opposite directions of the current, and to a difference in the contributions of scatterers from different sides of the quantum well to the resistance. It is shown that the difference between the resistances for different directions of the current is an effect with odd parity with respect to the direction of the magnetic field and that the magnitude of this effect increases as the current is raised. The behavior of the differences in the resistance for different directions of the current is observed as a function of the magnetic field strength and current. It is shown that the sign of this effect provides information on the ratio of the scattering intensities from the substrate side and the surface. [ABSTRACT FROM AUTHOR]

The magnetic and magnetoimpedance (MI) properties of a Permalloy-based thin-film structure, deposited onto a polymeric flexible substrate, are investigated as a function of the applied stress. The selected structure, a sandwich of NiFe/Ti multilayers with a central Cu layer, has been previously shown to produce extraordinary MI performance when deposited onto rigid substrates. Here, grown onto a cyclo olefin polymer substrate, it is evaluated as a deformation sensor and its properties analyzed in terms of the preparation conditions. A specially designed sample holder allows measuring simultaneously the hysteresis loop of the sample using magneto-optical Kerr effect and its MI using a network analyzer, while applying a controlled stress to the sample. The magnetoelastic anisotropy developed in the sample is longitudinal, revealing that the magnetostriction coefficient is positive, and competes with the transverse magnetic anisotropy induced during the sputtering deposition of the multilayer structure. The combined, effective anisotropy determines the shape of the hysteresis loop and the MI curves. We show how the evolution of the maxima of the MI curves with the applied stress allows a precise determination of the magnetostriction coefficient of the sample. The stress impedance is determined as the impedance change, measured at $H =0$ Oe, as function of the applied stress. It displays a linear behavior with a corresponding gauge factor of 60, thirty times larger than the one of conventional metallic strain gauges. [ABSTRACT FROM PUBLISHER]

Sensors based on giant magnetoimpedance effect are widely used in different technological applications. In this paper, a magnetoelastic sensor based on the changes of the high-frequency electrical impedance ( $Z$ ) of a soft magnetic sample under applied mechanical stress has been optimized to measure the cyclical diameter variations in plants (grapevines in particular) in order to characterize their water status. Micrometric trunk shrinkage and growth take place during daylight and night, respectively, due to the changes in transpiration process and in within-plant water balance in a daily basis. The characterization of these variations (usually performed through linear variable differential transducers) represents a powerful tool in the agronomic sector regarding irrigation plant schedule. [ABSTRACT FROM PUBLISHER]

Temperature dependence of giant magnetoimpedance (GMI) amorphous wires has been investigated in a quasi-industrial temperature range of [−20 °C; 120 °C]. Co-rich amorphous microwires, from Unitika Ltd, of $100~\mu $ m diameter and about 50 mm length were placed inside a regulated temperature chamber. The impedance modulus, as a function of the magnetic field, was measured using an impedance analyzer. The excitation current of the GMI wire was about 3 mA of amplitude and 1 MHz of frequency. In addition to the GMI ratio, particular attention was paid to the behavior of the intrinsic sensitivity and the offset, which are the most relevant quantities in a real GMI sensor implementation. The experimental results have showed that the impedance curve was changed with the temperature. The maximum sensitivity and the GMI ratio increased with temperatures ranging from −20 to 80 °C. Then, beyond 80 °C, the trend seemed to be reversed. Over the considered temperature range, and at typical bias field of H = 35 A/m, the intrinsic sensitivity varied with a temperature coefficient of 0.4%/°C, while the temperature coefficient of the offset was about 200 nT/K. [ABSTRACT FROM PUBLISHER]

The implementation and the performance of a software-defined radio (SDR) detector for the signal demodulation and processing in off-diagonal GMI sensors are presented. One of the underlying ideas of this SDR is to benefit from the possibility to obtain almost linear and asymmetric characteristics of the off-diagonal component around the zero field. Unlike the commonly used peak detectors, the implemented SDR detector allows retaining this feature, without using any bias field and additional techniques of offset canceling. The key rules for a successful implementation of the SDR detector are given in some details and its potential is addressed. The first performances of the sensor are given and discussed. These include response, sensitivity, and noise as well as dynamic range, linearity, and slew rate. [ABSTRACT FROM PUBLISHER]

In recent years, the number of magnetic sensors introduced into complex electronic devices has rapidly increased due to the growing request for automatic systems. Giant magnetoimpedance (GMI) sensitive elements show very high sensitivity with respect to the applied magnetic field and in wire geometry they can be obtained using massive and cheap technologies. Although GMI of electroplated wires has been studied for years, many important points have not been analyzed in the case of short wires or complex configurations. In this paper, the structure, quasi-static magnetic properties, GMI (1–200 MHz range), and microwave absorption phenomena (0.1–18 GHz range) were studied in Cu98Be2/Fe19Co17Ni64electroplated wires. GMI was also comparatively analyzed for different configurations of the sensitive elements with one or two wires. [ABSTRACT FROM PUBLISHER]

Cobalt-based amorphous alloys, in particular CoFeBSi, have been widely used to study the response of ac-impedance to the external dc magnetic field, i.e., the so-called Giant Magneto Impedance (GMI) effect. The utility of CoFeBSi in different applications such as field-sensitive sensors is known and practiced. Despite the wealth of experimental studies on GMI properties of CoFeBSi alloys, no computational approach has yet been addressed on electronic and magnetic properties of these systems at nanoscales. In this study, we have computed electronic and magnetic properties of amorphous CoFeBSi alloys using a combined Molecular Dynamics (MD) and Density Functional Theory (DFT) approach. MD is used to provide a physically realistic sampling of different atomic configurations while the properties such as dipole moments and magnetic susceptibilities are computed using DFT. Our study shows a wide spectrum of electronic as well as magnetic properties for nanoclusters of different sizes having implications for rational design of Co-based ferromagnetic alloys. [ABSTRACT FROM AUTHOR]

Dual-Ion Beam Assisted Deposition is a suitable method for the preparation of giant magneto-impedance (GMI) materials. In this paper, Co 73 Si 12 B 15 thin films with different thicknesses were prepared by Dual-Ion Beam Assisted Deposition, and the influences of film thickness on magnetic properties and GMI effect were investigated. It was found that the asymmetric magnetic hysteresis loop in the prepared Co 73 Si 12 B 15 thin films occurs at ambient temperature, and the shift behavior of hysteresis loop associated with film thickness. With the film thickness increasing, the values of shift field and coercive field and other parameters such as remanence and shift ratio appeared complex variation. At a certain frequency, the large GMI effect is only observed in some films, which have good magnetic properties including low coercivity, low remanence ratio and high shift ratio. The results indicated that the thickness dependence of magnetic properties nonlinearly determined the GMI effect in Co 73 Si 12 B 15 thin films. [ABSTRACT FROM AUTHOR]

We investigate the quasi-static magnetic, magnetotransport, and dynamic magnetic properties in ferromagnetic biphase films with distinct non-magnetic metallic spacer layers. We observe that the nature of the non-magnetic metallic spacer material does not have significant influence on the overall biphase magnetic behavior, and, consequently, on the magnetotransport and dynamic magnetic responses. We focus on the magnetoimpedance effect and verify that the films present asymmetric magnetoimpedance effect. Moreover, we explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the probe current frequency in order to achieve higher sensitivity values. The invariance of the magnetic behavior and the asymmetric magnetoimpedance effect in ferromagnetic biphase films with distinct non-magnetic metallic spacers place them as promising candidates for probe element and open possibilities to the development of lower-cost high sensitivity linear magnetic field sensor devices. [ABSTRACT FROM AUTHOR]

The detailed magnetic study of complex 3 d -electron based Fe 3 Ga 4 is reported. It undergoes paramagnetic to antiferromagnetic ( T N ) and antiferromagnetic to ferromagnetic ( T C ) transitions respectively around 380 and 70 K. The thermal hysteresis of field-cooled cooling (FCC) and field-cooled warming (FCW) hints at first order phase transition below Curie temperature. A weak phase coexistence of ferro and antiferromagnetic phases is suggested by exploring the arrest-like first-order phenomenon. In the intermediate temperature range, field-driven metamagnetic transition from antiferro to ferromagnetic phase is confirmed. Further bringing the system very near to T N , field-induced transitions disappear and above T N predominant paramagnetic contribution is evident. The magnetic H – T phase diagram distinguishing different magnetic phases of Fe 3 Ga 4 is obtained. [ABSTRACT FROM AUTHOR]

We investigated tunneling anisotropic magnetoresistance (TAMR) at the interface between pentacene and La0.7Sr0.3MnO3 (LSMO) thin films prepared on SrTiO3 (STO) (110) substrates. The dependence of the TAMR ratio on the magnetic field strength was approximately ten times larger than that of the magnetic field angle at a high magnetic field. This large difference in the TAMR ratio is explained by the interface magnetic anisotropy of strain-induced LSMO thin films on a STO (110) substrate, which has an easy axis with an out-of-plane component. We also note that the TAMR owing to out-of-plane magnetization was positive at each angle of the in-plane magnetic field. This result implies that active control of the interface magnetic anisotropy between organic materials and ferromagnetic metals should realize nonvolatile and high-efficiency TAMR devices. [ABSTRACT FROM AUTHOR]

The equivalent magnetic noise spectral densities of off-diagonal giant magnetoimpedance (GMI)-based magnetometers exhibit significant low-frequency excess noise, proportional to $1/f$ noise. As it represents a serious limitation to the ultimate sensing performances of high sensitivity magnetometers, possible sources of this $1/f$ noise are under investigation. Low-frequency magnetization fluctuations have been proposed as the noise source in the case of classical GMI-based sensors. Here, we apply this model to off-diagonal GMI-based magnetometers. This requires the inclusion of magnetization fluctuation noise sources, in addition to white noise sources from electronic conditioning in the GMI effect equations. A pessimistic scenario is presented, predicting the upper limit of low-frequency excess noise from material characteristics. The equivalent magnetic noise level is then computed from the sensitivity of each term of the sensing element impedance matrix to the magnetization angle at the static working point (for both axial and circumferential static magnetic field) and to conditioning circuitry. Based on this, it appears that magnetization fluctuations similarly affect all modes of operation of the two-port network sensing element, inducing identical impedance fluctuations. It also appears that this noise depends only upon the static equilibrium condition. This condition is governed by the effective anisotropy of the magnetic wire and by both axial and circumferential static components of the working point. [ABSTRACT FROM AUTHOR]

• Co 68.15 Fe 4.35 Si 12.5 B 12 Cr 3 ribbons have great impedance ratio of 196% and high sensitivity of 114%/Oe. • Appropriate Cr replacing B improves the GMI effect and corrosion resistance of the ribbons. • The improved GMI effect is due to the reduced magnetic anisotropy and enhanced transverse permeability. • 4 at.% Cr deteriorates the amorphous forming ability and GMI effect of the ribbons. The effects of Cr doping and annealing temperature on the microstructure, soft magnetic properties, giant magneto-impedance (GMI) effect and corrosion resistance of Co 68.15 Fe 4.35 Si 12.5 B 15- x Cr x (x = 0, 1, 2, 3, 4 at.%) ribbons were investigated. Appropriate Cr content (≤3 at.%) effectively improves the thermal stability, magnetic softness, and GMI value of the ribbons, whereas more Cr deteriorates the magnetic properties owing to the precipitation of Co-Fe nanocrystals in the amorphous matrix. In addition, the corrosion resistance increases gradually with the increase of Cr content. The x = 3 ribbon annealed at 753 K exhibits low coercivity of 0.45 A/m, high permeability of 22,000 at 1 kHz, large GMI value of 196% at 5 MHz, and great sensitivity of 118%/Oe, which is superior to other ribbons. The variation of magnetic properties was explained by the change of magnetic anisotropy and permeability owing to the Cr doping and isothermal annealing. [ABSTRACT FROM AUTHOR]

Spin-dependent transport in two terminal zigzag silicene nanoribbon is investigated numerically in the presence of spin-orbit interactions, external spin splittings or exchange fields, and perpendicular electric field. We show by applying an exchange field, a tunable band gap emerges which depends on the exchange field vector angle with the plane of nanoribbon. Such behavior is interpreted using the low-energy Hamiltonian of the silicene which indicates qualitative agreement with results obtained from lattice model. Moreover, it is found that by decreasing the width of nanoribbon larger band gaps are achievable which can be promising for nanoelectronic applications. On the other hand, by imposing exchange fields inside the electrodes, the magnetoresistance of the junction is investigated. As a main result we observe that when the Rashba interaction becomes stronger the magnetoresistance decreases but it is not fully suppressed. Finally, in the presence of perpendicular electric fields applied to the electrodes, depending on their relative configuration, the so-called pseudomagnetoresistance is calculated. Our results indicates that the conductance of the silicene nanoribbon significantly differs between the parallel and anti-parallel configurations of electric fields in the electrodes. [ABSTRACT FROM AUTHOR]

Optimized giant magnetoimpedance effect of Fe 75.5 Cu 1 Nb 3 Si 13.5 B 7 amorphous ribbon/Fe 80 Ga 20 film composites has been investigated. FeCuNbSiB amorphous ribbons as the substrates are commercially available, magnetostrictive FeGa films are deposited on one or both sides of the ribbons by ion-beam sputtering. Compared with the GMI curves without FeGa layer, the GMI effect of FeCuNbSiB amorphous ribbon has been obviously improved with FeGa film covered (from 4% to 16%). Moreover, the details exhibit an interesting phenomenon: at a certain frequency, when the FeGa film covered on one side of the ribbon, the GMI ratio decreases with the thickness of the FeGa film; however, when the FeGa films covered on both sides of the ribbon, the GMI ratio increases with the thickness of the FeGa film. We mainly attribute the reason to strain-induced anisotropy, which is induced by magnetostrictive effect under a longitudinal applied magnetic field. [ABSTRACT FROM AUTHOR]

We report a systematic study of the influence of wire length, L, dependence of giant magneto-impedance (GMI) sensitivity of CoFeCrSiB soft magnetic amorphous wire of diameter ~100 µm developed by in-water quenching technique. The magnetization behaviour (hysteresis loops) of the wire with different length ( L = 1, 2, 3, 5, 8 and 10 cm) has been evaluated by fuxmetric induction method. It was observed that the behaviour of the hysteresis loops change drastically with the wire length, being attributed to the existence of a critical length, L , found to be around 3 cm. GMI measurements have been taken using automated GMI measurement system and the GMI sensitivities in terms of intrinsic impedance sensitivity ( S ) and voltage sensitivity ( S ) of the wire have been evaluated under optimal bias field and excitation current. It was found that the maximum ( S ) ≈ 0.63 Ω/kAm/cm and ( S ) ≈ 3.10 V/kAm/cm were achieved at a critical length L ~ 3 cm of the wire for an AC current of 5 mA and a frequency of 5 MHz. These findings provide crucial insights for optimization of the geometrical dimensions of magnetic sensing elements and important practical guidance for designing high sensitive GMI sensors. The relevant combinations of magnetic material parameters and operating conditions that optimize the sensitivity are highlighted. [ABSTRACT FROM AUTHOR]

We have proposed a series of novel tailoring techniques for integrating conventional vacuum annealing (CVA) and the specific (e.g. transverse- and rotated-) magnetic field annealing (as denoted by TMFA and RMFA respectively), and systematically investigated the impacts of them on the giant magnetoimpedance (GMI) properties and domain microstructure of Co-based amorphous wires. Experimental results indicated that a multiplex MFA treatment i.e, two-step CVA annealing under a rotated magnetic field of 4000Oe, can realize remarkable enhancement of GMI in comparison with the as-prepared, CVA-treated and MFA-treated wires. The GMI ratio increased firstly and then tended to be stable with increasing frequency, moreover, both permeability and GMI ratio decreased with the increase of DC magnetic field. At 13 MHz, the maximum GMI ratio [Δ Z / Z max ] max and field response sensitivity ξ max of RMFA-ed wires increased to 398.39% and 21.84%/Oe, respectively, which is 2.41 times and 3.17 times than those of 165.18% and 6.88%/Oe for the as-prepared wires. Essentially, the physical process of RMFA action is mainly described as the multi-angle induced magnetic anisotropy and atomic reordering dynamic process due to the co-action of rotatory variation magnetic field energy and thermal activation. Meanwhile, the GMI behavior of TMFA evolving from single peak (SP) to double peaks (DPs) is attributed to the increase of magnetic domain driving force (namely domain wall movement increment) and uni-directional inducing magnetic anisotropy at relatively high frequency, which modified the GMI ratio and field sensitivity to 334.61% and 33.51%/Oe, respectively. Therefore, it can be concluded that both RMFA & TMFA would be used to explore microwires with enhanced GMI property for high-performance sensor applications. [ABSTRACT FROM AUTHOR]

Microfluidic chip and giant magnetoimpedance (GMI)-related technology has developed quickly over the past decades in the field of biological detection. In this work, we designed and fabricated a GMI-based microfluidic system for screening of multiplex gastric cancer biomarkers. The microfluidic chip and GMI sensor were prepared by micro-electromechanical systems (MEMS) technology. This system can analyse 8 gastric cancer protein biomarkers simultaneously in less than 25 mins and offer more stable detection signal than conventional enzymological or fluorescent methods. The microfluidic chip was then tested in 150 clinical specimens and compared with enzyme-linked immunosorbent assay (ELISA) method. The results indicated no significant difference and excellent agreement. In short, the prototype of GMI-based microfluidic system has been developed successfully and showed promising potentials for parallel screening of cancer biomarkers. [ABSTRACT FROM AUTHOR]

Giant magnetoimpedance effect (GMI) in Co 68.15 Fe 4.35 Si 12.5 B 15 amorphous wire was studied in the presence of magnetite ferrofluid and without it. Magnetite nanoparticles for ferrofluid were prepared by the traditional wet chemistry co-precipitation method. GMI was measured in the frequency range of 2 to 6 MHz. The maximum value of GMI value of the ferrofluid covered amorphous wire was increased in all frequency intervals in comparison with GMI response of the wire non-covered by ferrofluid. These results open a new way of increasing magnetoimpedance effect value useful for sensor applications. [ABSTRACT FROM AUTHOR]

The bias magnetic field is generally used to set properly the operating point of the magnetic sensor based on the giant magneto-impedance effect (GMI sensor) as the GMI profile exhibits a nonlinear and unipolar dependence on the applied external magnetic field. However, the changes in sensing direction or position of the GMI sensor will induce a fluctuation in the output voltage signal by varying the bias magnetic field due to the uniform geomagnetic field without any magnetic shield. A scalar field GMI sensor using the self-regulating technology on the bias magnetic field is developed in order to overcome the output fluctuation. The self-regulating technology based on the principle of the feedback control can self-regulate the bias magnetic field so as to keep it in the initial state. The mathematical model and the detailed structure of the self-regulating system (SRS), and the structure of the magnetic detector are also investigated. It is demonstrated that the variation in the bias magnetic field can be effectively suppressed by the SRS and a relatively high stability is achieved in the output of the GMI sensor. It is suitable for the GMI sensor to be used in moving platforms such as vehicles, robots and portable instruments. [ABSTRACT FROM AUTHOR]

Giant magnetoimpedance (GMI) in the reentrant spin-glass (SG) phase of ferromagnetic Fe90Zr10 is reported. The temperature (T) dependence of the GMI allows the investigation of the spin dynamics in the SG phase in the MHz frequency regime and thus very short relaxation times τ (~10-8 s). The GMI shows a broad maximum around 150 K and diminishes with decreasing T below the glass temperature Tg of 15 K. The magnetic permeability data obtained from the GMI data show the general features observed in the ac magnetic susceptibility measured at lower frequencies (10≤f≤104 Hz), yielding values of Tf (=Tg(f)) that allow testing the validity of the power-law scaling used for describing the dynamics of SG-phases up to 15 MHz. A log-log plot of τ (=1/f) versus the reduced critical temperature shows two distinct regimes in the time-domain: (1) a critical slowing-down is observed for values τ > 3×10-3 s; and (2) for 7×10-8≤τ≤3×10-3 s. In the latter case a fitting to the power-law yields the value 7.4 for the product of the critical exponents zv, and 1.6×10-7 s for the microscopic relaxation time τ0. The product of the exponents is appropriate for an Ising spin glass. [ABSTRACT FROM AUTHOR]

The assembled domain structure model (ADSM) is applied to an analysis of thin film magneto impedance (MI) element. The ADSM is a multiscale magnetization model constructed by the assembly of mesoscopic particles called the simplified domain structure models. The ADSM successfully reconstructs the characteristics of the thin film MI element where three stable magnetic domain states coexist. The simulation reveals the influence of longitudinal distribution of magnetic field on the magnetization property that is hardly affected by the perpendicular magnetic field. [ABSTRACT FROM AUTHOR]

In this paper, a multilayer thin-film giant magnetoimpedance (GMI) magnetic sensor is fabricated, and its performance is enhanced by post-processing treatment. The CoSiB alloy is developed to enhance the performance of multilayer thin-film GMI sensors. The material is studied for different post-processing magnetothermal conditions. The provided recipe will facilitate low-cost fabrication of GMI structures in conventional microfabrication facilities. A detailed study is carried out to investigate the effect of temperature, time, and external magnetic field on the results of the post-processing technique. The prepared samples are tested with various magnetics and material characterization tools in order to give a detailed understanding of these effects. The post-processing shows a significant impact on the magnetic properties of the material. It is demonstrated that some nanoclusters of cobalt (with a diameter of 2–4 nm) form in its amorphous matrix structure, enhancing the permeability of the material. [ABSTRACT FROM PUBLISHER]

We report on a method for ultrasensitive detection and quantification of the pathogen Escherichia coli ( E. coli), type O157:H7. It is using a tortuous-shaped giant magnetoimpedance (GMI) sensor in combination with an open-surface microfluidic system coated with a gold film for performing the sandwich immunobinding on its surface. Streptavidin-coated super magnetic Dynabeads were loaded with biotinylated polyclonal antibody to capture E. coli O157:H7. The E. coli-loaded Dynabeads are then injected into the microfluidics system where it comes into contact with the surface of gold nanofilm carrying the monoclonal antibody to form the immunocomplex. As a result, the GMI ratio is strongly reduced at high frequencies if E. coli O157:H7 is present. The sensor has a linear response in the 50 to 500 cfu·mL concentration range, and the detection limit is 50 cfu·mL at a working frequency of 2.2 MHz. In our perception, this method provides a valuable tool for developing GMI-based microfluidic sensors systems for ultrasensitive and quantitative analysis of pathogenic bacteria. The method may also be extended to other sensing applications by employing respective immunoreagents. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A giant magnetoresistance (GMR) device formed by depositing two parallel nanosized ferromagnetic strips on top of a semiconductor heterostructure has been proposed theoretically (Zhai et al. in Phys Rev B 66:125305, ). For the sake of manipulating its performance, we introduce a tunable δ-potential into this device with the help of atomic-layer doping techniques such as molecular beam epitaxy (MBE) or metal-organic chemical-vapor deposition. We investigate theoretically the impact of such δ-doping on the magnetoresistance ratio (MR) of the GMR device. We find that, although the δ-doping is embedded in the device, a considerable GMR effect still exists due to the significant difference in electronic transmission between parallel (P) and antiparallel (AP) configurations. Moreover, the calculated results show that the MR of the GMR device varies sensitively with the weight and/or position of the δ-doping. Thus, the GMR device can be controlled by changing the δ-doping to obtain an adjustable GMR device for magnetoelectronics applications. [ABSTRACT FROM AUTHOR]

The treatment of perpendicular electric field upon γ-Fe2O3/MgO film at room temperature could adjust the magnetic properties (saturation magnetization, magnetic remanence, coercivity, and saturation magnetizing field) of the film. The enhancement of saturation magnetization after the treatment of electric field may be connected with the combined shift effects of Mg ions from MgO to γ-Fe2O3 and O2- ions from γ-Fe2O3 to MgO. The negative magnetoresistance of the γ-Fe2O3/MgO film also enhances with the treatment of perpendicular electric field at room temperature, possibly due to the increasing of electron hopping rate between Fe2+ and Fe3+. [ABSTRACT FROM AUTHOR]

Nuclear Magnetic Resonance (NMR) spectroscopy on small volumes, either on microfluidic channels or in vivo configuration, is a present challenge. We report here a high resolution NMR spectroscopy on micron scale performed with Giant Magnetic Resistance-based sensors placed in a static magnetic B0 field of 0.3T. The sensing volume of the order of several tens of pL opens the way to high resolution spectroscopy on volumes unreached so far. [ABSTRACT FROM AUTHOR]

We report the magnetic field dependence of electrical impedance Z in polycrystalline La0.75Ba0.25MnO3 a function of frequency from f = 1 MHz to 1 GHz at room temperature. The magnetoimpedance [MI = ΔZ/Z(0) where ΔZ = Z (H)-Z (0)] is -37.5 % (-58.5%) at 1(10) MHz for H = 1.2 kOe, which far exceeds mere -1.15% dc magnetoresistance. As f increases above 10 MHz, MI decreases in magnitude and changes sign from negative to positive. The change in sign of MI results from the transition of a single peak at H = 0 to two peaks at H = ± Hp accompanied by a minimum at the origin. Hp shifts towards higher field with increasing frequency. The occurrence of giant radio-frequency magnetoimpedance is promising for low-field sensor applications. [ABSTRACT FROM AUTHOR]

We report the magnetic field dependence of electrical impedance Z in polycrystalline La0.75Ba0.25MnO3 a function of frequency from f = 1 MHz to 1 GHz at room temperature. The magnetoimpedance [MI = ΔZ/Z(0) where ΔZ = Z (H)-Z (0)] is -37.5 % (-58.5%) at 1(10) MHz for H = 1.2 kOe, which far exceeds mere -1.15% dc magnetoresistance. As f increases above 10 MHz, MI decreases in magnitude and changes sign from negative to positive. The change in sign of MI results from the transition of a single peak at H = 0 to two peaks at H = ± Hp accompanied by a minimum at the origin. Hp shifts towards higher field with increasing frequency. The occurrence of giant radio-frequency magnetoimpedance is promising for low-field sensor applications. [ABSTRACT FROM AUTHOR]

We present studies of the interfacial layer between the metallic nucleus and glass coating in ferromagnetic Fe- and Co-rich microwires. Using a scanning electron microscope, we obtained the image of the interfacial layer and the elements distribution within the glass coating and metallic nucleus. This allowed us to estimate the thickness of the interfacial layer ( t). For both Fe- and Co-rich microwires, t ≈ 0.5 μm. We measured the frequency dependence of the giant magnetoimpedance ratio in Fe and Co-rich microwires, estimated the minimum penetration depth, and discussed the optimum frequency for different microwires considering the difference of the magnetic structure and the magnetic anisotropy inside the microwire and near the surface. [ABSTRACT FROM AUTHOR]

We investigate the magnetoelectric coupling and spin-polarized tunneling in Ni/KNbO 3 /Ni multiferroic tunnel junctions with asymmetric interfaces based on density functional theory. The junctions have two stable polarization states. We predict a peculiar magnetoelectric effect in such junctions originating from the magnetic reconstruction of Ni near the KO-terminated interface. This reconstruction is induced by the reversal of the ferroelectric polarization of KNbO 3 . Furthermore, the change in the magnetic ordering filters the spin-dependent current. This effect leads to a change in conductance by about two orders of magnitude. As a result we obtain a giant tunneling electroresistance effect. In addition, there exist sizable tunneling magnetoresistance effects for two polarization states. [ABSTRACT FROM AUTHOR]

We studied the effect of annealing conditions on magnetic properties of amorphous CoFeNi-based glass-coated microwires. We showed that annealing can be very effective for manipulation of the magnetic properties of amorphous ferromagnetic glass-coated microwires. Low coercivity and high Gaint magnetoimpedance (GMI) effect have been observed in as-prepared Co-rich microwires. After annealing of Co-rich we can observe transformation of linear hysteresis loops to rectangular and coexistence of fast magnetization switching and GMI effect in the same sample. We demonstrated that the coercivity of microwires can be tailored by annealing in the range from 4 to 200 A/m. We found that the annealing considerably affects the magnetostriction coefficient and observed correlation between the magnetic hardening of studied microwires and the magnetostriction sign change. [ABSTRACT FROM AUTHOR]

Enhanced giant magnetoimpedance (GMI) effect has been observed in micro-patterned Co-based Metglas 2705M amorphous magnetic ribbons coated with single-layer graphene. The micro-patterned ribbon was designed for tortuous structure and fabricated by MEMS technology, and the graphene thin film was developed by spin coating and dispensing method onto the surface of ribbon. Relative to the plain ribbon, at a measured frequency of 6 MHz and a field of 20 Oe, a 13.1 % enhancement of the maximum GMI effect was observed in the ribbon by spin coating graphene. However, there was a small change of the GMI effect in ribbon coated graphene by dispensing method. AFM observation confirmed a smoother ribbon surface by spin coating graphene. The very large enhancement of the GMI effect is a consequence of reducing the ribbon surface roughness and the closed magnetic flux path under the graphene thin film layer. This result provides a potential thinking for designing high sensitivity, lightweight and flexible GMI sensor with graphene-based materials. [ABSTRACT FROM AUTHOR]

The effects of applied current annealing frequency, amplitude and magnetic field direction during alternative current-field annealing on giant magnetoimpedance (GMI) and magnetic properties of Co 68.15 Fe 4.35 B 12.5 Si 15 wire have been investigated. This annealing process leads to a complex domain structure because of the existence of the variable internal circumferential field and external static magnetic field. We have demonstrated that the applied current annealing with different frequencies, amplitudes and magnetic field directions can improve the magnetic properties and the GMI response. In the as-quenched wire, GMI max and saturation magnetization (M s ) are equal to 220% and 78.5 emu/g respectively. They grow up to 400% and 87.2 emu/g, respectively, while the amplitude of the 50 Hz annealing current is 400 mA and the applied magnetic field, perpendicular to the wire, cancels out the earth ' s magnetic field. In contrast, the samples annealed by 50 Hz (500 mA) and 100 kHz (400 mA) alternative currents show GMI max = 50% and 140%, and also M s = 41.8 and 40.7 emu/g, respectively. Altogether, our results show that alternative current-field annealing at appropriate conditions improves the GMI response and makes the samples more suitable for magnetic sensing. [ABSTRACT FROM AUTHOR]

Magnetic sensors are largely used in several engineering areas. Among them, magnetic sensors based on the Giant Magnetoimpedance (GMI) effect are a new family of magnetic sensing devices that have a huge potential for applications involving measurements of ultra-weak magnetic fields. The sensitivity of magnetometers is directly associated with the sensitivity of their sensing elements. The GMI effect is characterized by a large variation of the impedance (magnitude and phase) of a ferromagnetic sample, when subjected to a magnetic field. Recent studies have shown that phase-based GMI magnetometers have the potential to increase the sensitivity by about 100 times. The sensitivity of GMI samples depends on several parameters, such as sample length, external magnetic field, DC level and frequency of the excitation current. However, this dependency is yet to be sufficiently well-modeled in quantitative terms. So, the search for the set of parameters that optimizes the samples sensitivity is usually empirical and very time consuming. This paper deals with this problem by proposing a new neuro-genetic system aimed at maximizing the impedance phase sensitivity of GMI samples. A Multi-Layer Perceptron (MLP) Neural Network is used to model the impedance phase and a Genetic Algorithm uses the information provided by the neural network to determine which set of parameters maximizes the impedance phase sensitivity. The results obtained with a data set composed of four different GMI sample lengths demonstrate that the neuro-genetic system is able to correctly and automatically determine the set of conditioning parameters responsible for maximizing their phase sensitivities. [ABSTRACT FROM AUTHOR]

Classical magnetoresistance generally follows the quadratic dependence of the magnetic field at lower field and finally saturates when field is larger. Here, we report the large positive non-saturating linear magnetoresistance in topological crystalline insulator, Pb 0.6 Sn 0.4 Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. Magnetoresistance value as high as ∼200% was achieved at 3 K at magnetic field of 9 T. Linear magnetoresistance observed in Pb 0.6 Sn 0.4 Te is mainly governed by the spatial fluctuation carrier mobility due to distortions in the current paths in inhomogeneous conductor. [ABSTRACT FROM AUTHOR]

Thermo-ionic Vacuum Arc evaporation method was selected for the synthesis of Fe/Cu/Ni/Cu multilayer structures on Si (1 0 0) substrates. The aim of the study was the preparation and characterization of structures featuring a giant magnetoresistance effect. This was accomplished by inducing the formation of nanosized ferromagnetic crystallites in multilayer nonmagnetic solutions via atomic inter-diffusion processes by the tuning of deposition parameters. Layer-by-layer and inter-diffused type structures were prepared and comparatively analyzed by scanning electron microscopy, X-ray microanalysis, atomic force microscopy, X-ray diffraction and high-resolution transmission electron microscopy coupled with selected area electron diffraction. We presented the influence of the microstructure on electric and magnetic properties of the submicron-sized multilayers. The dependence of the electric resistance and the magnetoresistance on the composition, structure, morphology and roughness of the layers was established. We obtained an electric resistance value of 1.22 Ω for the layer-by-layer type structure, and 0.46 Ω for the inter-diffusion designed structure. Using the atomic inter-diffusion we succeeded in achieving an improvement of the magnetoresistive effect, from 0.1% to 2.3%. [ABSTRACT FROM AUTHOR]

Co68.25Fe4.5Si12.25B15 amorphous microwires with a diameter of 34 μm were prepared via the melt extraction method. The dependency of AC driving current Iac and frequency on giant magnetoimpedance (GMI) effect and magnetization were investigated using a 4294A impedance analyzer and the transverse Kerr effect. The GMI effect was analyzed when Iac changed from 6 mA to 20 mA at a frequency ranging from 0.1 MHz to 15 MHz. The influence of AC current dependent on the frequency is correlated with the magnetization mechanism. The maximum transverse Kerr intensity (MTKI) decreased with the increase in Iac under direct magnetic field when the frequency was below megahertz. However, MTKI values were similar with the increase of Iac when it was over 2 MHz. Meanwhile, the GMI effect was optimized by selecting an adequate value of AC driving current Ip, at which the circular permeability was higher when the frequency was not over 2 MHz. Results showed that the influence of Iac on magnetoimpedance became weak with strong skin effect and slightly stronger GMI effect driven by a higher Iac when the frequency was between 2 MHz and 15 MHz. The skin effect turned out to be the key factor to the GMI effect; thus, there were no obvious differences in magnetization and GMI effect with AC driving current changing when the frequency was as high as 15 MHz. [ABSTRACT FROM AUTHOR]

We studied the correlation between the magnetostriction coefficient, coercivity and Giant magnetoimpedance effect of Fe–Ni-rich microwires. As-prepared and annealed Fe 47.42 Ni 26.6 Si 11 B 12.99 C 1.99 microwires present rectangular hysteresis loops. Varying the time and the temperature of annealing we observed changes of the coercivity and Giant magnetoimpedance effect (GMI). Increasing the annealing time we observed first some magnetic softening and then magnetic hardening. These changes correlate with the evolution of the magnetostriction coefficient. Decreasing of the magnetostriction coefficient observed after annealing is related to formation of nanocrystalline structure. [ABSTRACT FROM AUTHOR]

We report on a theoretical study of the giant magnetoresistance (GMR) effect in a δ -doped magnetically confined semiconductor heterostructure nanostructure (MCSHN), which can be realized by depositing two nanosized ferromagnetic (FM) stripes on top and bottom of the semiconductor heterostructure and using the atomic layer doping technique. It is shown that such a nanosystem shows up a sizable GMR effect due to a significant discrepancy in transmission of parallel (P) and antiparallel (AP) magnetization configurations. It is also shown that the MR ratio varies sensitively with the weight and/or position of the δ -doping. Thus, one can conveniently tailor the degree of GMR effect by tuning the δ -doping, and such a nanosystem can be employed as a controllable GMR device for magnetic information storage. [ABSTRACT FROM AUTHOR]

The magnetoresistance of a heterostructure comprising parallel-connected epitaxial graphene on a metal substrate and graphene on a dielectric substrate has been studied in the framework of the Drude theory. The phenomenon of colossal magnetoresistance in this system is predicted on the basis of previous results for the conductivity of epitaxial graphene. [ABSTRACT FROM AUTHOR]